Speed control muffler with adjustable valve



United States Patent Stephen J. Gibel 5846 Edgerton Road, North Royalton, Ohio 44133 [21] App1.No. 818,169

[22] Filed March 21,1969

[45] Patented Dec. 15, 1970 [72] Inventor [54] SPEED CONTROL MUFFLER WITH ADJUSTABLE Primary ExaminerRobert S. Ward, Jr. Attorney-Ely, Golrick & Flynn ABSTRACT: Speed control muffler for exhaust of air-driven tools in which a porous metal casing, baffling sound waves of exhaust air, carries micrometrically adjustable valve, with slightly tapered head and seat, for precise control of air'flow to control speed of tool. One or more essential metal elements may be isolated from each other to aid in dissipation of sound energy by elastomeric elements confined between the relatively rigid metal elements.

248/15.22,24 [56] References Cited UNITED STATES PATENTS 1,251,655 1/1918 Gunnarson 18l/37X 1,935,202 11/1933 Chamberlainetal 181/33(.01)

low in passing through the SPEED CGNTROL MUFFLER WITH ADJUSTABLE VALVE This invention relates to an improved muffler for simultaneously muffling the sound of sharp impulses" of air exhausted from air-actuated tools and equipment while controlling the speed of such tools by controlling the rate of air flow into the muffler.

Pneumatically powered tools, particularly those exhausting intermittent charges of air during the tool s operation, characteristically emit sharp blasts which must be silenced to make the operations tolerable to the operators. Such mufflers must dissipate the attendant noise effectively, on the one hand, while, on the other, they must often be able to accurately and precisely control the rate of air flow into the muffler, since many pieces of pneumatically powered q equipment depend upon the control of back-pressure in the exhaust line for timing their operating cycles or speeds. In addition, these mufflers must be rugged to withstand the vibrational loads and stresses to which which they are subjected and they must also be compact, both to avoid cumbersome bulk and because of frequent space limitations on stationary equipment.

A sound-damping material which is peculiarly able to meet the above physical equipment of the foregoing types of muffler has been found to be sintered powderedmetal, such as bronze, which has a high degree of porosity. Though a piece of this material will be very brittle, soft, and weak (compared to a similar piece of the corresponding solid metal from which it is made), it can be molded in the course of sintering the metal powder so as to have sufficient mechanical strength to withstand the static and vibrational loads to which it will be subjected when used as casing or screen through'which the exhaust air is diffused. Due to the relative rigidity of the sintered powdered metal and the tortuous paths which the air must folpores of the metal, the material dampens the noise of the air by literally filtering out the sound waves. However, such brittleness and low mechanical strength make the material difficult to machine; a cutting tool, such as treading tap or die, rather than shearing the portion to be cut away, willtend to break the bonds between them the metal powder particles and/or peen the particles into the pores of the material. As a consequence, when it has been attempted heretofore to thread a powdered metal casing in a muffler so as to receive the threaded stem of a valve for controlling the flow of air into the muffler, the poor machining characteristics of the material have dictated that the threads be cut as coarsely as possible and, in no event, finer than standard coarse threads.

The result of the above-described practice of attempting to thread a powdered metal casing or element in a muffler so as to serve as the nut in which the threaded'stem of a speed-controlling valve is received has been that the coarse threads have made it difficult to obtain a precise adjustment of the valve. Further, since the threaded stem of the valve must be locked in its adjusted position, as by a jam nut, means must be provided for holding the threaded valve stem at or near its adjusted position while tightening the jam nut. In actuality, not only does such tightening of the jam nut tend to disturb the adjusted position of the valve stem, but an instinctive practice of operators is to make the final adjustment by torquing the jam nut so as to turn both the nut and the valve stem to the desired position of the valve stem. The resultant strain on the threads in the weak powdered metal casing strips them and thereby destroys the muffler.

An object and advantage of this invention is that it provides a muffler of simple, rugged, and compact construction using a powdered metal casing which carries a valve by which micrometric control of the air flow into the muffler is readily obtained without time-consuming fiddling by the operator; the valve may be readily locked in its adjusted position without inviting over-torquing of a jam nut, when such a locking means is employed, and, thereby minimizes breakage of the muffler. The structure of such a casing made according to this invention also permits modifications in which ajam nut may be eliminated as the valve locking means, the sintered metal casing may be readily replaced, when its pores become clogged by oil or like liquids and dust or other solid particles frequently entrained in the exhaust air, and such modifications may employ combined elastomeric elements which isolate relatively rigid metal elements from each other and thereby FIG. 3 is a view similar to FIG. 2, but showing various modifications which may be incorporated in a muffler em-,

bodying this invention.

As indicated in FIG. 1 showing the simplest commercial embodiment of a muffler 10 made according to this invention, themuffler comprises a pipe-threaded nipple portion 11 of solid material, such as brass or bronze, provided with a head 12 having nut faces by which the muffler may be securely mounted in a mating fitting carried by the end of the exhaust line of the tool or equipment to which it is attached.

The nipple portion 11 carries an outwardly extending casing 15 of porous sintered metal powders; these powders are usually but not necessarily always, brass, bronze, aluminum or like non ferrous metal, without excluding the use of sintered powders of ferrous metals such as for example, stainless steel (or even iron, where the possibility of weakening corrosion due to entrained pollutants in the muffled air is minimal) as well as mixed metal powders and other powders and binders by which porous so-called alloys of sintered and/or bonded powders and powdery materials are produced. Thus, it is conceivable that the casing 14 may be made of sufficiently porous, unglazed and incompletely vitrified ceramic material. The particular porous material for the casing 14, accordingly, is selected by those skilled in the art to provide adequate mechanical strength to withstand without rupture by the static and vibrating loads to which the unit can be reasonably expected to be subjected by the particular conditions where the muffler will be employed.

It is to be noted that the casing 15 is slightly conical, having a taper converging toward its outer end which carries a threaded stem 21 of the valve 26 provided with a screw driver slot 22, for example, whereby the stem 21 may be advanced or retracted and then locked in its adjusted position relative to the casing 15 by means of the jam nut 23. As shown in FIG. 1 the valve 20 is in its most advanced position, whereby it shuts off all entrance of air into the interior of the casing 15.

As shown in cross section in FIG. 2, the base of the nipple portion 11 is provided with a small internal shoulder 13 serving as a forward stop for the valve-seat insert 30 received and held within the base of the nipple by an interference or force fit. The head 12 is counterbored to provide a socket 19 receiving and seating the inner end of the casing 15, the casing being held in the socket 119 in this embodiment by a brazed joint, indicated as 16, in which the brazing metal flows into the clearance between the inner wall surface of the socket 19 and the outer tapered surface of the casing 15.

As shown in FIG. 2, the outer end of the casing 15 is closed by an end wall 17 which is substantially heavier-in the order of one and one-half to as much as four or five times-than the slightly conical side wall 18. This end wall 17 is drilled and tapped, preferably with a thread which is at least as fine as the national standard fine thread for the diameter of the threaded valve stem 21 received therein. Contrary to the prior practice of coarse threading porous sintered powdered metal, such as employed for the casing 15, not only may the casing be tapped to provide a fine thread, but the relatively deeper section of the end wall 17 may more than offset any weakness of a fine thread therein due to its interruption or fracture by a particle of metal powder being broken away by the thread-cutting tool. Thus, the stem 21, threaded nearly to the head 24 of the valve 20, will be securely held in the casing 15. I

The valve head 24 is provided with a slight outward taper; the deviation of this taper from the cylindrical is in the order of 2 and Vz (in case a coarse thread is employed on the stem 21) to 25- 30 (for very fine thread). The valve head 24 is received in and securely fits, in the most advanced position as shown, the correspondingly tapered bore 31 of the shouldered valve-seat insert 30. If an outer end portion 32 of the valveseat insert 30 extends into the casing 15, that end portion is preferably reduced in diameter to provide a clearance, as shown, to avoid interference with the tapered inner surface of the casing wall-18 during assembly when the seat 30 is driven home against the shoulder 13.'Such interference may otherwise arise from variations in thickness and/or out-of-roundness of the wall 18 which can occur in production molding of the porous powdered metal casing 15. i

The length of thread on the stem v2 1 is sufficient with respect to the inner depth of the casing 15, to allow the valve head 24 to be completely withdrawn from the seat 30 so as to provide substantially no obstruction to full flow of air through the valve seat bore 31 and its diffusion through the side wall 18; The minimum inner diameter of the casing is such as to permit such fullwithdrawal of the valve head 24; the inner depth of the casing is determined by the porosity of the metal with respect to thet ma'ximum expected flow of air through the bore 31 so as to provide sufficient areaperrnitting diffusion of air through the casing 15 when the valve is fully withdrawn without creating more than the maximum back-pressure tolerated by the tool or equipment served by the muffler. This is in contrast with prior art practice of designing the diffusing element of a muffler so as to provide an internal diffusing surface area having a direct ratio or range of ratios with respect to the bore of the entrance to the chamber constituted by or providing the diffusing element of the muffler.

' With a muffler as shown in FIGS. 1 and 2, one may readily obtain micrometric adjustment of air flow through the muf- .fler, andthereby precise control of the operational speeds or cycles of thetool or equipment to the exhaustof which the muffler is attached. When the desired precise adjustment is obtained, the operator can easily lock the valve in its adjusted position by tightening the jam nut 23 against the outer-end of the casing 15 without fear of significantly disturbing the adjustment due to a turning of the valve stem 21 at the final jamming of the nut 23. Indeed, because the valve may be locked in its adjusted position without significantly disturbing the adjustment, it thereby eliminates or minimizes the tendency of an operator. to over-torque the nut 23 and thereby destroy the muffler by stripping the threads in the porous metal casing. These advantages flow from the combination of the relatively fine thread on the stem 21 and/or the slight taper on the valve head 24 and'seat 31. For example, in a muffler made according to this invention and provided with a preferred taper of 5 from the cylindrical fof a valve head and seat bore when a standard fine thread is employed on a valve stem having a V4-28 NSF thread, and a valve head which seats in a bore having a minimum diameter of inch. one full turn of the valve stem 21 while the head 24 is positioned within the length of the bore 31 will effect an increase or decrease of the air flow above described in the amount of only .06 s .c.f./sec.

The above-described muffler as shown .in FIGS. 1 and 2 may be modified to retain all its advantages as set forth above while incorporating one or more of the structural variations of the embodiments se described below and shown in FIG. 3 of the drawings. The principal additional objects and advantages of this latter embodiment are essentially two-fold:

(a) In due time, as with all mufflers depending in whole or part upon diffusion of the exhaust air through a porous member, the pores eventually become so clogged with en trained oil and dust that the resultant back-pressure interferes with the effective operation of the tool or equipment being served. Due to the ineffectiveness and cost of backwashing with solvents and vapors, in such circumstances either the diffusing element or the entire muffler must be discarded and replaced; heretofore the latter has been the only practical alternative when the diffusing element has had to be permanently held in tension on the nipple fitting, such as by the brazing 16 shown in FIG. 2. For smaller sizes of mufflers made according to this invention, it is still more economical to discard the entire muffler,

but in larger sizes the cost of the molded sintered powments. which can be securely but replaceably attached to the nipple fitting.

(b) The desired and largely achieved effect of diffuser elements of porous powdered metal is to attenuate the sound .waves imposed upon the exhaust air expelled through the muffler in impulses or in a continuous flow. However, the direct contact between relatively rigid metallic elements, as shown in the embodiment of FIGS. 1 and 2 and in prior art mufflers, permits noise imparted by air to the mufflers attachment fitting before the air enters the diffusing chamber of the muffler to by pass the sound-attenuating effect of the air diffusing porous casing by direct conduction to the air surrounding the contacting metallic elements. As shown in FIG. 3, modification of this invention permits the isolation of one or all metallic elements by means of a confined elastomer and, thereby, avoiding or minimizing the transmission of noise attributable to direct contact between metallic elements, A further advantage of such isolation of the control valve from the porous metal casing is that it may eliminate the need for a jam nut or similar rigid locking means.

As shown in FIG. 3, the muffler is comprised of a nipple 111 similar to the nipple 11 of the embodiment shown in FIGS. 1 and 2 and having an internal shoulder 113. Instead of having nut faces as carried by the head 12, the nipple 111 is provided with a threaded head 112, counterbored to form a casing-receiving socket 119. The threads of the head 112 and pipe threads of the nipple portion 111 are preferably spaced to provide a portion 116 which, for purposes of disassembly, may be gripped with a lock wrench or narrow-jawed pipe wrench or provided with flats to be engaged by an open-jawed wrench. A molded casing of porous sintered powdered metal, having a side wall 118 and a heavier end wall 117 corresponding to walls 18 and 17 of the corresponding casing 15, is drilled to receive a grommet 123 of relatively soft nylon, plasticized vinyl chloride, silicone rubber, polyethylene, polypropylene, or other suitable elastomer (preferably thermoplastic) having a relatively low factor of restitution. As initially molded, the grommet 123 is a hollow cylinder having an external flange at one end; the other end is then spread open after insertion into the casing 115 to lock it securely therein.

The bore of the grommet 123 is slightly less than the outer diameter of the fine threaded stem 121 of the valve so as to serve as a self-locking nut for the stem when it is adjusted, as by means of a screw driver received in the slot 122. In addition, the grommet 123 can be threaded by the threads on the stem 121 as well as to isolate the valve from the casing. The head 124 of the valve 120 has a slight outward taper similar to that of the head 24 so as to fit and close, when the valve 120 is fully advanced, the mating tapered bore 131 of the valve seat insert 130. The valve seat insert 130, which may or may not have a reduced forward end 132 to provide clearance, is force-fitted into the bore of the nipple portion 111 against the shoulder 113 to secure it therein. Likewise, being of a suitable elastomer as shown in FIG. 3 and confined by the bore of the nipple portion 111 and shoulder 113, the insert serves as an internal sound dampener for the nipple fitting as well as a set seat for the micrometrically adjustable valve.

The casing 115 is removably secured in the muffler 110 by an internal threaded cap ring 140, preferably having nut faces or knurling (not evident in the sectional view of HO. 3) for assembly and disassembly, plus one or two O-rings depending upon whether insert 130 has a reduced forward end 132. If the insert'has such a forward end 132, as shown in FIG. 3, an ring 141 of a suitable elastomer is first inserted in the counterbore 119 and the inner end of the casing 115 is seated against it. A second elastomeric O-ring 142, fitting externally on the tapered casing wall 118, is engaged between the cap ring 140 and the outer end of the head 112, whereby tightening of the cap ring onthe head compresses both O-rings 141 and 142 and removably secures the casing 115 in the muffler. If the forward end of the insert 130 is not reduced, the O-ring 141 may be omitted, since tightening the cap ring and its confined O-ring 142 will sufficiently jam the internal tapered wall 118 on the insert 130 without seating the casing 115 against the base or wall of the counterbore 119. In either case, the casing 115 will be removably locked by confined elastomeric elements while being isolated from contact with the head of the nipple portion of the muffler.

The noise-reducing effect of the confined elastomeric elements in any one of the locations between metallic elements of the muffler, as shown in FIG. 3, is understood to be attributable to more than just the prevention of direct and, thus, soundconducting, contact between metallic elements; in addition, due to the relatively low modulus of elasticity of the elastomeric elements with respect to that of the metallic elements and, thus, the slower rate of sound conduction through them, such sound as would be conducted through them apparently physically works the elastomeric elements, particularly where they are confined between the more rigid metallic elements, whereby the energy of the noise is dissipated as heat.

lt is to be understood that this invention is not to be deemed limited to the specific embodiments disclosed, but may be otherwise modified by those skilled in the art without departing from the scope of the invention as defined in the following appended claims. For example, in either of the two embodiments disclosed, the nipple portions 11 and 111 and their respective valve seat inserts 30 and 130 may be integral, rather than separate elements as shown; in-the latter case, the integral'nipple portion and valve seat will be of an elastomer having sufficient mechanical strength to permit the muffler to be carried thereby and, thus, serving as the primary means of isolating the metallic elements of the muffler from the noise otherwise conducted by the usually metal exhaust line of the equipment being muffled.

lclaim: 1. A mierometrically adjustable speed control muffler comprising: line a connector means receivable on the end of the exhaust line of the equipment to be muffled; an outwardly extending casing having a wall comprised of a porous material, said casing providing an internal chamber receiving exhaust directly from the connector portion and from which chamber said exhaust diffuses through the porous wall of the casing; a valve comprised of a threaded valve stem extending through the outer end of said casing and having means for turning the same exteriorly of said casing, and a conical head on said valve having an outwardly divergent taper which does not exceed 30 from the cylindrical;

matingly threaded means receiving said threaded stem whereby the turning of said stem advances and retracts said valve in said casing; and

a valve seat having an axially extending tapered bore mating with said valve head; the depth and diameter of said chamber being sufficient to allow said valve head to be withdrawn therein to a position where it imposes no significant restriction on the flow of gases through said port and the porous wall of said chamber permits diffusion of the exhaust therethrough, when said valve head is withdrawn, without creating back-pressure which exceeds that which is tolerable for operation of the equipment to which the mufiler is attached.

2. A muffler as defined in claim 1 in which the porous material of the wall of said casing is sintered powdered metal, said casing carries the matingly threaded means in which said valve stem is received, and the threads of said valve stem have a pitch not exceeding the standard line thread for the diameter of said stem.

3. A muffler as defined in claim 2 in which said casing con sists of said porous sintered powdered metal attached to said connector means, and said means is comprised of a head portion receiving said casing and a nipple portion connecting the muffler to the exhaust line to be muffled.

4. A muffler as defined in claim 3 in which the casing is provided with an end wall portion having a greater depth os section than its side wall and the matingly threaded means receiving said valve stem constitute threads tapped in said end wall portion, and means are carried by said valve stem for locking said valve in an adjusted position.

5. A muffler as defined in claim 4 in which said connector means is of metal, the head portion is counterbored to receive said casing, and said casing is secured in said head portion by fused metal which has flowed at least partially into the clearance between said casing and the counterbore of said head portion.

6. A muffler as defined in claim 3 in which the matingly threaded means receiving said valve stem constitute a grommet comprised of elastomeric material and is received in the end wall of said casing, the bore of said grommet being sufficiently less than the outer diameter of the threads of said valve stem so as to serve as a self-locking nut for said valve stem.

7. A muffler as defined in claim 6 including a connector means having a head counterbored to receive said casing with clearance between the inner wall of said counterbore, the outer wall of said casing being conical with an outwardly convergent taper, an elastomeric ring carried on the outer wall of said casing and adapted to engage the head of said connector means, and a compression ring threaded on the head of said connector ring to compress said elastomeric ring between it, the said head, and the outer wall of said conical casing, whereby said casing will be removably secured to said connector means.

8. A muffler as defined in claim 7 in which said head portion carries an elastomeric valve seat extending into the said chamber and engages the inner wall thereof to prevent said casing from seating in said counterbore when said elastomeric ring is compressed.

9. A muffler as defined in claim 7 including a secured elastomeric ring engaged between said casing and said counterbore when said first elastomeric ring is compressed. 

